Blend IK and FK animation

Example of IK/FK blending

Blending the FK animation of a swinging arm with the IK animation of a waving arm.

A simple animation of a swinging arm during a walk cycle is created by selecting the root of an arm’s joint chain (the shoulder joint), rotating it along the Z axis, and then setting keys for the joint. This produces a rudimentary FK animation.

This FK animation sequence is blended with the directed motion of the arm waving by setting keys on the IK handle and the shoulder joint at the beginning and end of the FK animation, moving the current time indicator to create a blend region, changing the Ik Blend value to 1.000 (pure IK), and once again setting keys on the shoulder joint and IK handle. In the area between the pure FK and IK animation—the blend region, the IK Solver interpolates the animation from 0.000 to 1.000.

Pure IK animation is reached once the Ik Blend value is 1.000. The IK handle is then translated and rotated while setting keys, to produce the animation of the arm waving.

When the animation of the waving arm is complete, the animation is set back (using another blend region and changing the Ik Blend value to 0.000) to pure FK. The resulting animation resembles a swinging arm (FK) that rises into a wave (IK) and then descends back into a swinging motion (return to FK).

Example

To insert IK within FK animation (whether or not the FK is controlled by Set IK/FK Key)

1. Open the Animation menu set (press F2).
2. At the first frame of the time range where you want to insert IK, select the IK handle and set a key by selecting Animate > IK/FK Keys > Set IK/FK Key.
3. At the end frame of the time range where you want to insert IK, select the IK handle and set a key by selecting Animate > IK/FK Keys > Set IK/FK Key.

   We refer to the keys you set in the prior two steps as bounding keys, because they ensure that any keys you set between them will not change the animation outside their range.

4. Turn on Animate > IK/FK Keys > Enable IK Solver.
5. Manipulate the IK handle and use Set IK/FK Key as desired for the frames between the bounding keys.

To insert FK within IK animation controlled by Set IK/FK Key

1. Open the Animation menu set (press F2).
2. At the first frame of the time range where you want to insert FK, select the IK handle and set a key by selecting Animate > IK/FK Keys > Set IK/FK Key.
3. At the last frame of the time range where you want to insert FK, select the IK handle and set a key by selecting Animate > IK/FK Keys > Set IK/FK Key.

   We refer to the keys you set in the prior two steps as bounding keys. They ensure that any keys you set between them will not inadvertently change the animation outside of their range.

4. Turn off Animate > IK/FK Keys > Enable IK Solver.
5. Rotate the desired joints and use Set IK/FK Key as necessary for the frames between the bounding keys.

To insert FK within IK animation not controlled by Set IK/FK Key

1. Open the Animation menu set (press F2).
2. At the first frame of the animation, select the IK handle, turn on Solver Enable, and set a key for Solver Enable.
3. At the end frame of the time range where you want to insert FK, select the IK handle and set a key by selecting Animate > IK/FK Keys > Set IK/FK Key.
4. At the first frame of the time range where you want to insert FK, select the IK handle and set a key by selecting Animate > IK/FK Keys > Set IK/FK Key.

   We refer to the keys you set in the prior two steps as bounding keys. They ensure that any keys you set between them will not inadvertently change the animation outside of their range.

5. Turn off Animate > IK/FK Keys > Enable IK Solver.
6. Rotate the desired joints and use Set IK/FK Key as necessary for the frames between the bounding keys.

After FK animation, a joint chain may flip to an undesired position when you turn on Animate > IK/FK Keys > Enable IK Solver. To undo the joint flipping and prevent it from occurring when you turn on Enable IK Solver, do the following:

To eliminate unexpected joint flipping after turning on the IK Solver

1. Open the Animation menu set (press F2).
2. Undo the Enable IK Solver menu item to return the joint chain to the position it had before flipping.
3. Select the IK handle.
4. Select Skeleton > Set Preferred Angle.
5. Select Animate > IK/FK Keys > Enable IK Solver.
6. Select Animate > IK/FK Keys > Set IK/FK Key.

   Continue using IK as desired.

Related topics

• Forward kinematics (FK)
• Inverse kinematics (IK)
• IK/FK blending
• Animate > IK/FK Keys > Set IK/FK Key
• Ik Blend
• Ik Fk Control